Method of producing silvery pig iron



June 27, 1961 A. H. DIERKER 2,990,271

METHOD OF PRODUCING SILVERY PIG IRON Filed April 8, 1960 IN VEN TOR.

ARTHUR H. DIERK ER BY N MAHONEY, MILLER a RAMBO ATTORNEYS United States Patent 2,990,271 ,7 METHOD OF PRODUCING "SILVERY PIG IRON Arthur H. Dierker, 939 King Ave., Columbus 12, Ohio FiledApr. 8, 1960, 'Ser. 'No. 20,917 1 Claim. (Cl. 75-41) My invention relates to a method of producing silvery pig iron.

As is well known, silvery pig iron is an iron silicon alloy or a ferro silicon with a silicon content ranging from 6 percent to 18 percent. This relatively higher silicon content distinguishes silvery pig iron from the standard grades of pig iron which normally contain from 0.80 percent to 4 percent silicon. Silvery pig iron is made both in blast furnaces and in electric furnaces. The presset invention deals with the 'productionof silvery pig iron in blast furnaces.

At the present time, in the smelting of silvery pig iron in a blast furnace, the higher silicon content of the prodnot is normally achieved by using a more siliceous slag, a higher blast temperature, and a higher coke rate than would be used in the production of the usual low-silicon grades of pig iron. As would be obvious to experienced blast furnace operators, the adoption of the foregoing practices results in reduced production rates. Since more coke or more heat or a more siliceous slag, or some combination of these, is required to increase the silicon content of the iron being made in the blast furnace, the production of the furnace falls off as the silicon content in the iron being produced is increased.

Market conditions normally require the producer of blast furnace silvery pig iron to make iron of a number of different silicon contents within -a relatively short period of time. This means that for each change of grade or specification, the furnace burden must be changed and, consequently, in the swing from one grade or specification to the other, a certain amount of intermediate grades of iron is produced. Frequently, there is no market for these intermediate grades with the result that there is an accumulation, on the part of the producer, of slow-moving or dead inventory.

By using the process I have invented, the blast furnace may be burdened and operated to produce one of the lower grades of silvery pig iron and be kept on this burden and operating procedure so as to maintain maximum production. At the same time, the silicon content of the iron being produced in the blast furnace can be increased to any desired level without changing the furnace burden or operating practices and without producing any undesirable intermediate grades of iron.

In the accompanying drawing, I have illustrated apparatus capable of carrying out my process but it is to be understood that this is merely an example of one apparatus which can be utilized in connection with my process.

According to my process, the furnace is burdened to produce pig iron at one of the lower silicon levels, for example, 8 percent. If a product of higher silicon content is required, the additional silicon content is obtained by injecting ferro silicon into the furnace proper at some suitable point in the smelting zone or below it, that is, below the oxidizing zone Where it will not be lost, in whole or in part, by oxidation which would occur if added at the top of the furnace. The added ferro silicon melts in the furnace and combines with the descending iron in the furnace. The resultant iron accumulating in the hearth of the furnace then has a higher silicon content than would be achieved without the injection of the ferro silicon in the manner indicated above. By this 2,990,271 Patented June 27, 196-1;

2 method, any desired silicon content, (for example, within the usual range of 6 to 18 percent, can be produced.

It is preferred that the ferro silicon injected into the furnace be of the commercially available 50 percent grade since this can be'obtained at the lowest cost per unit'of silicon. However, other grades of ferro silicon can be used. For example, grades ranging from 20 percent to 98 percent can be used in the process although it is not economical to use the grades near the minimum or maximum of the range. The ferro silicon should be inpar'ti'cle or lump size ranging from A" to 3", preferably /2" to 2". Recovery is poor on finer sizes and larger sizes are difficult to feed into thefurnace.

The introduction of ferro silicon can be accomplished most conveniently by arranging a specially constructed blow pipe "aheadof the tuyere that will permit introducing the ferro silicon, in a suitable size, at a regulated rate into the stream of heated air or hot blast that is flowing continuously through the tuyere. The blast, in turn, will carry the ferro silicon into the furnace proper where it will be melted and intimately mixed with the downcoming flow of reduced iron.

With reference to the drawing, I have illustrated equipment of the type actually used in performing my process. The ferro silicon of suitable size is stored in the hopper 1 which discharges onto a rotatable table 2. The table 2 is rotated slowly and, as it rotates, the deposited ferro silicon is swept off by a stationary plow 3 into a funnel 4 which, in turn, channels the material into the tube 5. In the tube 5, the ferro silicon is hit by a stream of compressed air issuing from a pipe 6 which is connected to a suitable source. This stream of compressed air is of sufiicient velocity and pressure to drive the material down through the tube 5 and prevent the hot blast from the blow pipe 8 back-ing up into the tube. In case the equipment is stopped or the supply of compressed air fails, a quick-acting valve 7 is closed to prevent this hot blast from flowing back to the tube 5 and escaping at the open end thereof. From the tube 5, the ferro silicon drops into the blow pipe 8 where it is picked up by the hot blast and carried through the tuyere 9 into the hearth area of the blast furnace 10. The bustle pipe 11 applies hot blast to several tuyeres through the elbow 12. Although the drawing illustrates only one tuyere, it is well known that blast furnaces are equipped usually with six or more tuyeres. The ferro silicon is preferably fed through at least two diametrically opposed tuyeres although it may be fed through any desired number of tuyeres at angularly spaced intervals around the furnace.

As indicated above, the drawing illustrates one method only of feeding ferro silicon into the furnace and other devices can be used equally well in the practice of my invention.

Following are the results of an actual blast furnace 111311 for producing silvery iron by the process described a ove.

During this run, the furnace was burdened and operated in a manner that normally would have produced an iron having a silicon content of 8.75 percent. During the run of slightly better than four days, 62,720 pounds of ferro silicon was fed through one tuyere at a uniform rate. The ferro silicon had an average silicon content of 49.44 percent and was in a size range from V2" to 1 /2". During the run, 2,256,300 pounds of iron was produced with an average silicon content of 9.958 percent.

Statistics available for a four-year period of operation of the same blast furnace show an average production per day of 203.95 gross tons for irons ranging from 9.51 percent to 10.00 percent silicon. During the indicated experimental run of 4.2 days, the average production was if 72,990,271 r The calculated increase in i} production was 35.85 gross tons per day or an increase-of-- 17.58 percent.

Irons of higher silicon content be produced from the same burden by increasing the feed rate through the one tu'yere or by feeding the same rate through more'than one tuyere; t Y I I f Itz-w'ill be apparent from the above description that with the process disclosed above, the-blast furnace can be burdened and Operated to .p'rodu'ce'one of the lower grades of silvery 'pig iron and be kept on this burden and operating procedure. Any time it is necessaryto produce an'iron of a higher grade, the silicon content of the iron being produced by the furnace can be increased by adding" the'ferro silicon, in the manner indicated, without changing the furnace burden or practices and without producing any undesirable intermediate grades of iron during the changeover. The capacity of the furnace is maintained even though a higher grade silvery pig iron is produced, since the furnace can be operated under-its original burden and operating conditions with the increased silvery content beingobtained by the addition of the ferro silicon in the manner described. .1 According to the provisions of the patent statutes, the

' principles of this invention have been explained and have been illustrated and described in what is now considered to represent the best embodiment. However, it is to be understood that, within the scope of the appended claim, the invention may be practiced otherwise than as specifically illustrated and described. a Having thus described my invention, what I claim is: A process of,operating a blast furnace'to maintain maximum production of a selected grade. of. silvery pig iron, which comprises burdening the furnace with a charge to produce a grade of pig iron with a silicon content less than that desired in'the finalproduct train the furnace and introducing with thehot blast ofthe furnace, ferro silicon in lump size ranging from A to 3""int0 the interior of the furnace at a point where-it is melted and combines with the descending molten iron in the furnace so that the molten mixture will be carried down r into the hearth where it will accumulate as a bath having the desired higher silicon content. 20

f References Cited in the file of patent UNITED STATES PATENTS n Kuro Kanamori et a1. Dec. 2;, 195g 

